our justice correspondent pete williams has been following the investigation all day. he's in our d.c. newsroom tonight. pete, good evening. >> reporter: brian, good evening. the fbi is pursuing very promising leads. one in particular tonight thanks to the abundance of pictures and videos rounded up in the two days since the bombing. we are getting a close-up look at how the bombs were made. >> guys, guys, guys. no way. >> reporter: the fbi says it is getting exactly what it asked for. pictures from several sources showing someone carrying a heavy backpack or duffel bag and placing it at the spot where one bomb went off. one of the most promising images, they say, comes from a department store surveillance camera high up on a building, able to look down at the crowd. on a day when incorrect news reports of an arrest distracted officials, investigators were working aggressively to discover, find, and interview that person. that's at the scene of the second bombing following the first by about 15 seconds. it's that second spot shown on this picture sent to nbc station wh